They are similar because:
Both set in university
There's a love triangle between the female and male lead and one of the 2nd male leads
Both of them talk about growing up and being young
The male lead is a bit of a jerk and is arrogant
Rich boy/poor girl drama
4 male leads who are popular at th euniversity
The relationship btw the female and male lead is similar

Differences:
None of the male leads knew each other before becoming roommates in Hi Flower
There are more business/ company feuds in Hi Flower
The female lead is an orphan and struggles to support her and her brother's education.

Both dramas are quite sweet and has a cute couple as the main leads. The female leads of both dramas are tricked into marrying with someone that has a bad reputation and both know how to cook. In Hua Jian Ti Hu Fang Da Chu, the male lead acts like a gangster, he's rude, doesn't do anything but visit the brothel or picking fights. In My Amazing bride, the male lead has an IQ of a child. Both male leads become desirable husband/ spouse material during the drama through the efforts of the female lead. However, Hua Jian Ti Hu Fang Da Chu is more carefree and fluffy and the leads have a happier relationship throughout the drama. In My amazing Bride, the drama is a little more tragic and the couple faces more obstacles in their relationship.